Body area network technology to transmit and receive communication data via a living body such as a human body is developed in various fields. In the body area network, a communication apparatus utilizing the human body as part of a transmission line is provided with two electrodes. One of the electrodes is a signal electrode connected to a signal line, while the other of the electrodes is a reference potential electrode having a reference potential and being connected to a ground potential of the communication apparatus. The communication apparatus transmits a potential difference between the signal electrode and the reference potential electrode to another communication apparatus with their signal electrodes coupled together mainly via a human body and the reference potential electrodes coupled together mainly via space or earth.
The signal electrode is disposed inside a housing, taking into account entry of water, surface deterioration, wear, and the like. In this case, capacitive coupling between the human body and the signal electrode is via the housing, thus leading to varying distances from the human body surface. Therefore, there is a problem of causing a decrease in electric field components perpendicular to the human body surface and hence a deterioration in transmitting/receiving performance. Also, there arises a problem that the housing decreases in strength because of coming in direct contact with the human body.